The data for the pages was contained in the “flyback”; each dot of each frame of your normal TV programme image started at the top left of the screen, moved to the right and then flew back to the left, one line down until you had a screen’s-worth. The flyback was fast so as to get a full screen image in whatever the frame rate was (30Hz?) Originally the flyback was just wasted bandwidth: a necessary loss whilst your TV moved it’s electron beam back to the left hand side. But because the flyback was fast, you’d never be able to get a full ‘proper’ image in there; that’s why teletext was text and primitive block graphics. And why you’d have to wait several minutes to see the page you wanted on a trend page cycle!
The data for the pages was contained in the “flyback”; each dot of each frame of your normal TV programme image started at the top left of the screen, moved to the right and then flew back to the left, one line down until you had a screen’s-worth. The flyback was fast so as to get a full screen image in whatever the frame rate was (30Hz?) Originally the flyback was just wasted bandwidth: a necessary loss whilst your TV moved it’s electron beam back to the left hand side. But because the flyback was fast, you’d never be able to get a full ‘proper’ image in there; that’s why teletext was text and primitive block graphics. And why you’d have to wait several minutes to see the page you wanted on a trend page cycle!